The present study will examine the behavioral effects of cholecystokinin-octapeptide (CCK8). It has been suggested that CCK8 might have neuroleptic properties because it has been shown to coexist with dopamine in certain mesolimbic pathways that have been implicated in schizophrenia. Recent experiments have shown that CCK8 meets some of the behavioral criteria for neuroleptic drugs such as the impairment of conditioned-avoidance responding. However, CCK8 has been shown to be less potent than the reference drug haloperidol. The present study will test various CCK8 in order to find more potent, long-lasting molecules. Also, an examination of structure-activity relationships will shed light on what part of the CCK8 molecule determines its bioactivity. A second objective is to compare peripheral and intraventricular injections of CCK8 to determine if CCK8 exerts its effects directly on the central nervous system or if it acts via a peripheral mechanism. The effects of CCK8 will be determined by training rats in a conditioned avoidance paradigm and observing responding after varying doses of peptide. In the first experiment rats will be trained on a Sidman avoidance paradigm to run back and forth in a shuttle box to avoid electric shock. Following training, rats will be divided into 25 groups and given intraperitoneal injections of saline, CCK8, CCK8 analogues, pentagastrin, or ceruletide in doses varying from .160 to 1.280 mg/kg. In a second experiment rats will be trained on the avoidance task and then implanted with cannulae aimed at the lateral ventrical. After surgery rats will be given intraventricular of intraperitoneal injections of saline or CCK8. A direct central effect would be suggested by a greater effect on avoidance at a lower dose following intraventricular injection.